Allergy is a hypersensitive state induced by an exaggerated immune response to a foreign agent, such as an allergen. Immediate (type I) hypersensitivity, characterized by allergic reactions immediately following contact with the allergen, is mediated via B cells and is based on antigen-antibody reactions. Delayed hypersensitivity is mediated via T cells and based on mechanisms of cellular immunity. In recent years, the term “allergy” has become more and more synonymous with type I hypersensitivity.
Immediate hypersensitivity is a response based on the production of antibodies of the immunoglobulin class E (IgE antibodies) by B cells which upon exposure to an allergen differentiate into antibody secreting plasma cells. The IgE induced reaction is a local event occurring at the site of the allergen's entry into the body, i.e. at mucosal surfaces and/or at local lymph nodes. Locally produced IgE will first sensitize local mast cells, i.e. IgE antibodies bind with their constant regions to Fcε receptors on the surface of the mast cells, and then “spill-over” IgE enters the circulation and binds to receptors on both circulating basophils and tissue-fixed mast cells throughout the body. When the bound IgE is subsequently contacted with the allergen, the Fcε receptors are crosslinked by binding of the allergen causing the cells to degranulate and release a number of anaphylactic mediators such as histamine, prdstaglandins, leukotrienes, etc. It is the release of these substances which is responsible for the clinical symptoms typical of immediate hypersensitivity, namely contraction of smooth muscle in the respiratory tract or the intestine, the dilation of small blood vessels and the increase in their permeability to water and plasma proteins, the secretion of mucus resulting, e.g in allergic rhinitis, atopic excema and asthma, and the stimulation of nerve endings in the skin resulting in itching and pain. In addition, the reaction upon second contact with the allergen is intensified because some B cells form a “memory pool” of surface IgE positive B cells (slgE+ B cells) after the first contact with the allergen by expressing IgE on the cell surface.
There are two major receptors for IgE, the high affinity receptor FcεRI and the low-affinity receptor FcεRII. FcεRI is predominantly expressed on the surface of mast cells and basophils, but low levels of FcεRI can also be found on human Langerhan's cells, dendritic cells, and monocytes, where it functions in IgE-mediated allergen presentation. In addition, FcεRI has been reported on human eosinophils and platelets (Hasegawa, S. et. al., Hematopoiesis, 1999, 93:2543-2551). FcεRI is not found on the surface of B cells, T cells, or neutrophils. The expression of FcεRI on Langerhan's cells and dermal dendritic cells is functionally and biologically important for IgE-bound antigen presentation in allergic individuals (Klubal R. et al., J. Invest. Dermatol. 1997, 108 (3):336-42).
The low-affinity receptor, FcεRII (CD23) is a lectin-like molecule comprising three identical subunits with head structures extending from a long α-helical coiled stalk from the cellular plasma membrane (Dierks, A. E. et al., J. Immunol. 1993, 150:2372-2382). Upon binding to IgE, FcεRII associates with CD21 on B cells involved in the regulation of synthesis of IgE (Sanon, A. et al., J. Allergy Clin. Immunol. 1990, 86:333-344, Bonnefoy, J. et al., Eur. Resp. J. 1996, 9:63s-66s). FcεRII has long been recognized for allergen presentation (Sutton and Gould, 1993, Nature, 366:421-428). IgE bound to FcεRII on epithelial cells is responsible for specific and rapid allergen presentation (Yang, P. P., J. Clin. Invest., 2000, 106:879-886). FcεRII is present on several cell types, including B-cells, eosinophils, platelets, natural killer cells, T-cells, follicular dendritic cells, and Langerhan's cells.
The structural entities on the IgE molecule that interact with FcεRI and FcεRII have also been identified. Mutagenesis studies have indicated that the CH3 domain mediates IgE interaction with both FcεRI (Presta et al., J. Biol. Chem. 1994, 269:26368-26373; Henry A. J. et al., Biochemistry, 1997, 36:15568-15578) and FcεRII (Sutton and Gould, Nature, 1993, 366: 421-428; Shi, J. et al., Biochemistry, 1997, 36:2112-2122). The binding sites for both high- and low-affinity receptors are located symmetrically along a central rotational axis through the two CH3 domains. The FcεRI-binding site is located in a CH3 domain on the outward side near the junction of the CH2 domain, whereas the FcεRII-binding site is on the carboxyl-terminus of CH3.
A promising concept for the treatment of allergy involves the application of monoclonal antibodies, which are IgE isotype-specific and are thus capable of binding IgE. This approach is based on the inhibition of allergic reactions by downregulating the IgE immune response, which is the earliest event in the induction of allergy and provides for the maintenance of the allergic state. As the response of other antibody classes is not affected, both an immediate and a long lasting effect on allergic symptoms is achieved. Early studies of human basophil density showed a correlation between the level of IgE in the plasma of a patient and the number of FcεRI receptors per basophil (Malveaux et al., J. Clin. Invest., 1978, 62:176). They noted that the FcεRI densities in allergic and non-allergic persons range from 104 to 106 receptors per basophil. Later it was shown that treatment of allergic diseases with anti-IgE decreased the amount of circulating IgE to 1% of pretreatment levels (MacGlashan et al., J. Immunol., 1997, 158:1438-1445). MacGlashan analyzed serum obtained from patients treated with whole anti-IgE antibody, which binds free IgE circulating in the serum of the patient. They reported that lowering the level of circulating IgE in a patient resulted in a lower number of receptors present on the surface of basophils. Thus, they hypothesized that FcεRI density on the surface of basophils and mast cells is directly or indirectly regulated by the level of circulating IgE antibody.
More recently, WO 99/62550 disclosed the use of IgE molecules and fragments, which bind to FcεRI and FcεRII IgE binding sites to block IgE binding to receptors. However, effective therapies that lack deleterious side effects for the management of these allergic diseases are limited. One therapeutic approach to treating allergic diseases involved using humanized anti-IgE antibody to treat allergic rhinitis and asthma (Come, J. et al., J. Clin. Invest.1997, 99:879-887; Racine-Poon, A. et al., Clin. Pharmcol. Ther. 1997, 62:675-690; Fahy, J. V. et al., Am. J. Resp. Crit. Care Med. 1997, 155:1824-1834; Boulet, L. P. et al., Am. J. Resp. Crit. Care Med., 1997, 155:1835-1840; Milgrom, E. et al., N. Engl. J. Med., 1999, 341:1966-1973). These clinical data demonstrate that inhibition of IgE binding to its receptors is an effective approach to treating allergic diseases.
Antibodies suitable as anti-allergic agents should react with surface IgE positive B cells which differentiate into IgE producing plasma cells, so that they can be used to functionally eliminate those B cells. However, antibodies to IgE in principle may also induce mediator release from IgE sensitized mast cells by crosslinking the Fcε receptors, thus antagonizing the beneficial effect exerted on the serum IgE and slgE+ B cell level. Therefore, antibodies applicable for therapy of allergy must not be capable of reacting with IgE bound on sensitized mast cells and basophils, but should retain the capability to recognize slgE+ B cells.
Such IgE isotype-specific antibodies have been described e.g. by Chang et al. (Biotechnology 8, 122-126 (1990)), in European Patent No. EP0407392, and several U.S. patents, e.g., U.S. Pat. No. 5,449,760. However, as the disclosed antibodies are not of human origin they are less suitable for application to humans due to their immunogenicity as foreign proteins. This drawback may potentially be reduced by transforming, e.g., a rodent anti-IgE monoclonal antibody into a chimeric antibody which combines the variable domains of the rodent antibody with human antibody constant domains. This approach conserves the antigen-binding site of the rodent parent anti-IgE antibody, while conferring the human isotype and effector functions. The immunogenicity of a chimeric antibody can be further reduced by grafting rodent hypervariable regions, also termed complementarity determining regions (CDRs), into the frameworks of human light and heavy chain variable region domains resulting in reshaped human antibodies. The technique involves the substitution or recombinant grafting of antigen-specific rodent CDR sequences for those existent within “generic” human heavy and light chain variable domains (U.S. Pat. No. 6,180,370).
Natural intact immunoglobulins or antibodies comprise a generally Y-shaped tetrameric molecule having an antigen binding-site at the end of each upper arm. An antigen binding site consists of the variable domain of a heavy chain associated with the variable domain of a light chain. More specifically, the antigen binding site of an antibody is essentially formed by the 3 CDRs of the variable domain of a heavy chain (VH) and the 3 CDRs of the variable domain of the light chain (VL). In both VL and VH the CDRs alternate with 4 framework regions (FRs) forming a polypeptide chain of the general formulaFR1-CDR1-FR2-CDR2-FR3-CDR3-FR4 (I),  (i)wherein the polypeptide chain is described as starting at the N-terminal extremity and ending at the C-terminal extremity. The CDRs of VH and VL are also referred to as H1, H2, H3, and L1, L2, L3, respectively. The determination as to what constitutes an FR or a CDR is usually made by comparing the amino acid sequences of a number of antibodies raised in the same species and general rules for identification are known in the art (“Sequences of proteins of immunological interest”, Kabat E. A. et al., US department of health and human service, Public health service, National Institute of Health).
The contribution made by a light chain variable domain to the energetics of binding is small as compared with that made by the associated heavy chain variable domain, and isolated heavy chain variable domains have an antigen binding activity on their own. Such molecules are commonly referred to as single domain antibodies (Ward, E. S. et al., Nature 341, 544-546 (1989)).
The CDRs form loops which, within the domains, are connected to a β-sheet framework. The relationship between amino acid sequence and structure of a loop can be described by a canonical structure model (Chothia et al., Nature 342, 887-883 (1989)). According to this model, antibodies have only a few main-chain conformations or “canonical structures” for each hypervariable region. The conformations are determined by the presence of a few key amino acid residues at specific sites in the CDRs and, for certain loops, in the framework regions. Hypervariable regions that have the same conformations in different immunoglobulins have the same or very similar amino acid residues at these sites.
CDR grafting has been carried out for monoclonal antibodies yielding humanized human antibodies with a binding affinity significantly lower than that of the rodent CDR-donor antibody. Findings have indicated that, in addition to the transfer of CDRs, changes within the framework of the human sequence may be necessary in some instances to provide satisfactory antigen binding activity in the CDR-grafted product.
Queen et al. (Proc. Natl. Acad. Sci. USA 86, 10029-10033 (1989)) disclosed that the CDRs from a murine anti-Tac monoclonal antibody could be grafted into a human framework. The human frameworks were chosen to maximize homology with the murine sequence. The authors used a computer model of the murine parent antibody to identify amino acid residues located within the FRs that are close enough to interact with the CDRs or antigen. These residues were mutated to the residue found in the murine sequence. The humanized anti-Tac antibody had an affinity that was only about ⅓ that of the murine anti-Tac antibody and maintenance of the human character of this antibody was problematic.
Treatment of diseases with very high levels of IgE may require an antibody with higher affinity to reduce the risk of immunogenicity, and to expand the clinical indications to diseases with very high levels of IgE, e.g., atopic dermatitis. Thus, it is desirable to have an anti-IgE antibody with greater level of humanization and much higher affinity for IgE. The antibodies in this invention are anti-human IgE antibodies with ultra high affinities and a higher degree of human sequence homology lowering the risk of immunogenicity.
Thus, there is a need for higher affinity humanized antibodies that will allow lowering the amount of antibody necessary to treat disease, thereby lowering the potential side-effects from immunogenicity of the drug and the cost to the patient. Morover, the present invention improves the probability that high affinity antibodies will be identified.